1. Field of the Invention
The invention relates to a digital electrophotographic copying apparatus, and, particularly relates to a digital image-storing electrophotographic copying apparatus in which image data from an original document are stored before being printed.
2. Discussion of the Related Art
A digital image-storing electrophotographic copying apparatus having a document reading means, an image storage means for temporarily storing image data obtained from the document reading means, and an image printing means for producing printed copies according to an electrophotographic process based on the image data stored in the image storage means is known in the art. This type of copying apparatus typically performs electronic recirculating document handling (hereinafter referred to as "electronic RDH"), forward/reverse outputting, sample copying, and other functions.
However, the conventional digital image-storing electrophotographic copying apparatus is expensive and used mainly for super-speed applications. As a result, power is supplied to this type of copying apparatus through a custom or exclusive scheme of electrical wiring. Electric power is, therefore, not usually a constraint upon copying apparatus performance.
However, a growing demand exists for a medium-speed, digital image-storing electrophotographic copying apparatus which may be connected to an electrical outlet in a typical office environment. In view of this demand, the production of a medium-speed, image-storing copying apparatus capable of being powered by a range of standard electrical supplies poses several technical problems.
Power supply control techniques used in the conventional image-storing electrophotographic copying apparatus simultaneously distribute power to the reading means (typically a read scanner) and the printing means, because the reading operation and the printing operation are carried out at substantially the same time. This type of conventional copying apparatus also typically provides a larger quantity of electric power to the copier fuser during heating periods than is ordinarily provided during normal copying operation in order to facilitate increased copying speeds.
As a means of optimizing electric power supply during operation, the prior art teaches a method of temporarily switching OFF an exposure light source during the return period of a scanner in order to redirect the light source power to the scanner servomotor. However, in a medium-speed apparatus (40 copies or more per minute) the exposure light source generally requires a rise time of about 50 to 200 msec. This exposure light source rise time is sufficiently short, as compared with the time required to return the scanner (about 2 to about 300 msec), to preclude switching OFF the exposure light source as a means of optimizing the electric power supply. Accordingly, it is difficult to use conventional methods of redistributing the quantity of electric power used by the exposure light source to the scanner servomotor. Consequently, no improvement in printing speed can be realized using the method.
The aforementioned problem of improving printing speed within a predetermined range of standard electrical power supplies exists in digital and analog image-storing electrophotographic copying apparatuses.